The present invention relates to a lithium secondary battery, in which a positive active material is lithium manganese oxide, which has excellent charging and discharging cycle properties.
In recent years, miniaturization and reduction of weight has been accelerated for such portable electronic instruments as a portable phone, a VTR, and a note-type PC. As a cell for an electric power source, a secondary battery, in which complex oxide made of lithium and a transition element, carbon material, and an organic electrolyte solution prepared by dissolving an Li ion electrolyte in an organic solvent are used for the positive active material, negative active material, and the electrolyte, respectively, is being used.
Such battery is normally named as lithium secondary battery or lithium ion battery and has features of a high energy density and a high single-cell voltage as about 4 V. Thus, the lithium secondary battery attracts attention as an electric power source of not only said portable electronic instruments, but also electric vehicles (hereafter, EV) or hybrid electric vehicles (hereafter HEV) which are expected to become popular to the public as a low pollution automobile on the basis of the latest environmental problems.
In such a lithium secondary battery, cell capacity and charge and discharge cycle properties (hereafter, cycle properties) largely depend on material characteristics of the positive active material used. Here, the complex oxide made of lithium and a transition element used as the positive active material is specifically exemplified by lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium manganese oxide (LiMn2O4) or the like.